The present invention relates to detection of chemiluminescent radiation in the cleaning of substrate processing chambers.
In substrate fabrication processes, semiconductor, dielectric, and conductor materials, such as for example, polysilicon, silicon dioxide, aluminum and or tungsten silicide, are formed on a substrate by chemical vapor deposition (CVD), physical vapor deposition (PVD), oxidation, nitridation, ion implantation, and may be subsequently processed by etching processes. For example, in a typical CVD process, a reactive gas is used to deposit material on the substrate, and in a PVD process, a target is sputtered to deposit material on the substrate. In oxidation and nitridation processes, an oxide or nitride material, such as silicon dioxide or silicon nitride, respectively, is formed on the substrate by exposing the substrate to a suitable gaseous environment. In ion implantation processes, ions are implanted into the substrate. In etching processes, a patterned etch resistant mask of photoresist or oxide hard mask is formed on the substrate by lithographic methods, and the exposed portions of the substrate are typically etched by an energized gas to form patterned gates, vias contact holes or interconnect lines.
In such processes, it is often desirable to use a process monitoring method to monitor and control processing of the substrate to predetermine process stages or process endpoints. For example, it may be desirable to stop etching when a layer of material is etched through or etched slightly beyond its thickness (a small depth into the underlying material). It may also be desirable to stop a deposition, oxidation or nitridation process when a predetermined thickness of material is obtained.
Process endpoint detection may also be used to determine an endpoint of a chamber or substrate cleaning process. When substrates have been processed in a process chamber, process residues may be formed on the chamber or substrate surfaces. The chamber performance and the substrate contamination levels may be improved by preventing or removing accumulation of the process residues on the chamber surfaces. The residues on the substrate may also need to be cleaned prior to subsequent process steps. It is desirable, therefore to have a monitoring system which can accurately determine a process endpoint, or the point at which the process residues are adequately cleaned from the chamber or substrate surfaces.
Typical process monitoring methods detect a radiation emanating from the chamber to monitor the process and determine a process endpoint. These methods include, for example, plasma emission analysis in which an emission spectrum of a plasma in the chamber is analyzed to determine a spectral change that arises from a change in the material being etched—which may occur upon etching through a material—as for example taught in U.S. Pat. No. 4,328,068 which is incorporated herein by reference. Another example, U.S. Pat. No. 5,362,256, which is also incorporated herein by reference, discloses a method of monitoring a process by monitoring a plasma emission intensity at a selected wavelength and correlating variations in the plasma emission intensity with a process endpoint. However, plasma emission analysis occurs as a gas phase reaction in the plasma which may require chemical species to migrate from the substrate or chamber surface to the plasma environment. As a result, there may be a time lag between the process performed on a surface in the chamber, such as the substrate or chamber surface, and the detectable gas phase plasma emission. Also, plasma emission analysis is dependent upon a plasma being generated in the chamber.
Thus, it is desirable to have a process monitoring method and apparatus capable of monitoring a process, for example, to detect an endpoint of the process, such as a chamber cleaning process within the chamber. It is further desirable to have a process monitoring system which does not require the process gas to be energized to obtain detectable radiation emissions.